Time measuring system



Jan. 24, 1939. THLJDIM ND 2,144,873

TlME MEASURING SYSTEM Filed May 4, 19:54

INVENTOR y 7. L. D/MOND B ATTORNEY Patented Jan. 24, 1939 UNITED STATESPATENT OFFICE TIME MEASURING SYSTEM Application May 4, 1934, Serial No.723,882

Claims.

This invention relates to improvements in time measuring systems andmore particularly to the utilization in such systems of gaseousconductor or discharge tubes for the purpose of providing a 5 simple andeffective means for determining the passage of a predetermined intervalof time.

The gaseous conductor or discharge tubes utilized in the arrangements ofthis invention are tubes filled with a low pressure gaseous contentwhich, for purposes of illustration, might be neon, argon, helium,mercury vapor or combinations of gases of this group. Such tubes havethe characteristic of breaking down and becoming conductive on onevoltage and remaining in such a conductive state on a much lowervoltage. It is one of the primary features of this invention therefore,to utilize a discharge tube of the above type in combination with acondenser and resistance so that the breakdown potential on the tube maybe controlled through the potential on the condenser, the charging timeof which is made equal to the time interval to be'measured. If the timeinterval elapses before the breakdown potential of the tube is reached,the condenser is short-circuited or otherwise prevented from attaining ahigher voltage by the interval-producing means and the tube preventedfrom flashing. On the other hand if the time interval is longer than thetime taken to charge the condenser to the breakdown potential of thetube said tube is caused to flash, the visible luminosity of whichfurnishes the signal that the time interval is longer than itspredetermined value.

Another feature of the invention relates to an arrangement whereby theresistance in series with the condenser is calibrated in terms of thetime taken to break down the tube so that once the resistance iscalibrated in terms of this time interval for any known voltage supplyand tube break down potential, it remains fixed thereafter for all othervoltage changes and tube break down variations and compensationstherefor will be made over a separate variable resistance that controlsthe potential across the condenser and across the tube.

The time-measuring circuit itself is based on the following twophenomena: (1) The potential across a condenser being charged in serieswith a resistance element is a function of the time the voltage isapplied to the series combination of the ohmic resistance of saidresistance element and of the capacity of the condenser; (2) Tubes ofthe character described have a definite break- 55 down voltage at whichpoint the tube emits light.

In these circuits the charging of the condenser is started at thebeginning of the time interval to be measured. If the charging voltageon the condenser reaches the breakdown voltage of the tube before thecharging of said condense-r is stopped by the contacts that produce thetime interval to be measured, a momentary glow in the tube will benoted. If the resistance is now varied until the glow is just preventedfrom occurring it will be known that the resistance is 10 of such avalue as to allow the condenser to reach a potential practically equalto the break down voltage of the tube. Since the voltage which thecondenser attains is constant and a function of the time and theresistance (other 15 things remaining equal), the resistance in serieswith the condenser may be thus calibrated in units of time.

A clearer conception of the scope and purpose of the invention may beobtained from the fol- 20 lowing description taken in connection withthe attached drawing and appended claims. In the drawing, I representsthe contacts whose open period is to be measured, 2 the timingcondenser,

3 a resistance in series with said condenser, 4 the 25 neon or similarlamp, 6 the time calibrated resistance, I and ID the elements of apotentiometer,

8 a battery, 9 a variable resistance, and II a switching key.

As said before, my invention makes use of the 30 well known electricalprinciple that in a circuit that involves a capacity C in series withtwo ohmic resistances R1 and R2 in a closed circuit with a source ofbattery E, then the voltage Va across the terminal of the circuit a-a,as shown, 35 and the voltage Va across the plates of the condenser 2 aregoverned by the relation where R=R1+R2 and t=time taken to raise thevoltage across the plates of the condenser to the value Vc.

The gas-filled glow lamp 4 is shunted across 45 the plates of thecondenser so that the voltage across the condenser is impressed upon theelements of the lamp.

When the breakdown voltage of the lamp is reached the lamp will glowwhile the condenser 50 is discharging. If the open periods of contact Iare constant and recurrent, R1 (resistance 6) can be varied until thelamp just fails to glow on account of the short-circuiting of thecondenser 2 by contact I. Under such conditions the voltage reached bythe condenser will be practically equal to the breakdown voltage Vb ofthe lamp.

are kept constant, the time 1. will vary directly with the resistance Rand R may be calibrated in units of time. In the circuit shown in thediagram, since resistance 3 is fixed, only resistance 6 would be variedand calibrated in terms of time units.

The constant ratio between voltage Vb and Va is attained by varying thevoltage across the potentiometer by means of variable resistance 9. Tomeasure a time with this circuit key N is operated, contact I is openedand resistance 9 is varled until the lamp glows. The potentiometer isthen delivering a voltage Vb across the terminals of the circuit aa, asmeasured by the fixed resistance [0 of said potentiometer. Key H is nowreleased and resistance 6 (R1) is now adjusted, while contact I isdelivering the open period to be measured until lamp 4 glows. When thishappens, the value of resistance 6 indicates the time interval. Thereason for this is in the fact that resistance I of the fixedpotentiometer has a fixed ratio to resistance ID of said potentiometer.Then, assuming the voltage to vary linearly with the total resistance ofthe potentiometer, the ratio of the total voltage supplied through bothresistances of. the potentiometer, that is, resistances l and I0, is aconstant multiplied by the value of the voltage supplied only throughresistance l0. That is,

Then, according to Equation (6), the value of R (i. e. resistance 6)will measure the time interval, and may be calibrated as such fromFormula 1.

In the circuit above described, it is assumed that the potentiometerresistance is low compared to R1. Otherwise the time indicated will varywith the voltage used. If it is desired to have the time vary with thevoltage, this can be accomplished since R1 can be made large if C ismade small.

The above arrangements and methods for compensating the voltage and tubevariations by a resistance which controls the potential across thecondenser and across the tube can be applied to any circuit arrangementfor measuring the time interval of the operation of any two contacts,such as for instance, the break interval as in the illustration, or themake interval, or the interval between the break of one set of contactsand the make of another, or between two sets of makes 01'- two sets ofbreaks,.etc.

What is claimed is: l j

1. The method of measuring a time interval which consists in applying apotential across the plates of a condenser during the time interval tobe measured, discharging said condenser through a glow lamp when saidcondenser reaches a potential equal to the breakdown potential of saidlamp and adjusting the charging rate of said condenser until said lampjust fails to glow upon the expiration of the time interval whereby thedegree of adjustment becomes a measure of the time interval.

2. In a device for measuring a time interval, a condenser, a source ofpotential, a circuit for charging said condenser from said source, meansfor rendering said charging circuit eiiectiveduring the time interval tobe measured, a glow lamp in shunt of said condenser through which saidcondenser discharges when said condenser becomes charged to thebreakdown potential of said lamp, and a variable resistance foradjusting the charging rate of said condenser until said lamp just failsto glow upon the expiration of the time interval whereby said resistancebecomes a measure of the time interval.

3. In a device for measuring a time interval, a

condenser, a source of potential, a circuit for charging said condenserfrom said source, means for rendering said charging circuit effective atthe start of the time interval and for rendering said circuitineffective at the end of said interval, a glow lamp in shunt of saidcondenser through which said condenser discharges when said condenserbecomes charged to the breakdown potential of said lamp, and a variableresistance for adjusting the charging rate of said condenser until saidlamp just fails to glow at the end of said time interval whereby saidresistance becomes a measure of the time interval. Y 4. In a device formeasuring a time interval, a condenser, a source ofpotential, a circuitfor charging said condenser from said source, means responsive to thestart of said time interval for rendering said charging circuitefiective, means responsive to the end of the time interval forrendering said charging circuit ineffective, a glow lamp in shunt ofsaid condenser through which said condenser discharges when saidcondenser becomes charged to the breakdown potential of said lamp, and avariable resistance for adjusting the charging rate of said condenseruntil said lamp just fails to glow at the end of said time intervalwhereby said resistance becomes a measure of the time interval.

5. A device for measuring the duration of an electrical energy impulsecomprising a measuring circuit including a glow discharge tube whichemits light upon the app ication of a given voltage thereto, acondenser, adjustable means to impress upon said condenser a voltagederived from the impulse which during the impulse period charges thecondenser for attainment of its maximum potential at the end of theimpulse period and to impress said potential upon said glow tube, meansto adjust said derived voltage to a value which will cause saidpotential when at maximum to be substantially equal to the emissionvoltage of said tube, and means to determine the ratio of said derivedvoltage and said potential.

THOMAS L. DIMOND.

